1. Field of the Invention
The present invention relates to a method of and apparatus for generating a cylinder discriminating signal in a distributor for an internal combustion engine.
2. Description of the Related Art
FIG. 4 shows a conventional distributor for an internal combustion engine. In the figure, the reference numeral 1 denotes a distributor housing, 2 a cap, 3 a rotary shaft rotated synchronously with the internal combustion engine, 4 a reluctor for a cylinder discriminating signal which is rotated together with the rotary shaft (hereinafter referred to as "cylinder discriminating reluctor"), 5 a sensor disposed to face the reluctor 4 so as to generate a cylinder discriminating signal when the rotary shaft is rotated, 9 a reluctor for detecting ignition timing (hereinafter referred to as "ignition timing reluctor"), 10 a stator constituting a part of the magnetic circuit of the ignition timing reluctor, and 30 a vacuum spark advance plate to which the stator 10 is attached (it should be noted that the mechanism for activating the vacuum spark advance plate 30 is not shown). The reference numeral 6 denotes a magnet signal type generator for generating an ignition signal for each of the cylinders, 7 an ignition timing control unit for controlling the ignition signal generated from the magnet signal type generator 6 on the basis of the positional relationship between the reluctor 9 and the stator 10, that is, according to whether or not the reluctor 9 and the stator 10 face each other, 8 a centrifugal spark advance controller, 81 a governor base fixed to the rotary shaft, 82, 83 weights, and 84 a centrifugal spark advance plate. The reference numeral 11 denotes a spark advance sleeve loosely fitted on the rotary shaft 3. The ignition timing reluctor 9 is attached to the spark advance sleeve 11. The sensor 5 is attached to the outer surface of the cylindrical part of the distributor housing 1 in such a manner that the sensing surface 51 of the sensor 5 is exposed in the housing 1. The cylinder discriminating reluctor 4 is fixed to the governor base 81 of the centrifugal spark advance controller 8. The functional part of the cylinder discriminating reluctor 4 approaches and passes the sensing surface 51 of the sensor 5 when the rotary shaft 3 is rotated together with the reluctor 4.
In the case of a four-cylinder engine, the rotary shaft 3 is rotated one full turn per two full turns of the crankshaft (not shown) of the engine, so that four ignition timing signals and one cylinder discriminating signal are output per one full turn of the shaft 3. A cylinder which is defined as a standard is detected by the cylinder discriminating signal from the sensor 5, and the signal is supplied to a fuel injecting device corresponding to the cylinder so that fuel is injected when the valve of the cylinder is opened. Then, ignition is conducted on the basis of the ignition timing signal for each of the cylinders.
In the above-described conventional distributor, the ignition timing signal IG which is generated by the reluctor 9 is advanced with respect to TDC of the engine crank angle, whereas the cylinder discriminating signal G generated by the reluctor 4 is not advanced, as shown in FIG. 5. Therefore, in order to enable the signal G to overlap the signal IG so as to detect a cylinder, the width .theta..sub.A of the signal G must be greater than the entire range of spark advance, i.e., .theta..sub.1 +.theta..sub.2, where .theta..sub.1 is the maximum centrifugal spark advance and .theta..sub.2 is the maximum vacuum spark advance. For this reason, the width of the functional part of the reluctor 4 must be .theta..sub.A, as shown in FIG. 3b. Accordingly, the width of the signal generated by the combination of the cylinder discriminating reluctor 4 and the sensor 5 is disadvantageously wide, and the wide reluctor 4 leads to an increase in the amount of imbalance during rotation.